Yes, sorry for your problem but no-shows automatically invalidate everything else. If you decide to cancel part of a trip due to unexpected events, train strikes or whatever that is not directly under control of the airline itself you must contact them and make sure they will not cancel the rest (including the return flight).
Leaving aside the no-show rule, which doesn't make much sense to me, this situation is a good example of an accountability sink.
The intermediary I booked the tickets with made an obvious mistake and showed the wrong airport code. Maybe the airport opening was meant to happen earlier, and the intermediary had already updated their emails or something like that. They refused to do anything meaningful and did not even acknowledge their mistake.
The fact that I was compensated by the airline that had nothing to do with this mistake is even more astonishing to me, although they were obviously protecting their brand reputation.